Technical Field
This disclosure relates to a fixing device to fix an unfixed image on a recording medium and an image forming apparatus incorporating the fixing device.
Description of the Related Art
In fixing devices employing an induction heating system, an excessive temperature increase of excitation coils might hamper compliance of safety standards or cause disconnection of the excitation coils. In order to prevent such an excessive temperature increase, use of a cooling fan is proposed to cool down the excitation coils.
However, the temperature of the excitation coils may increase when high electric power is input. Therefore, such use of a cooling fan needs a greater output power of the cooling fan sufficiently to cool down the excitation coils, causing problems such as increases in production costs, power consumption and noise. Although use of heat insulation materials or the like may increase cooling efficiency, a configuration of a fixing device including such heat insulation materials is complicated and increases the production costs. In order to prevent such an increase in the production costs, there is a need for a configuration to increase cooling efficiency of an excitation coil without significantly changing a typical configuration of fixing device.
In an induction heating unit of the fixing device, the excitation coil is disposed facing, e.g., a fixing roller or a heating roller, over which a fixing belt is stretched, to heat the fixing roller or the heating roller. Therefore, conductive wires, such as a conductive wire of a coil thermostat and/or a conductive wire of a sensor to detect a temperature of the fixing roller, are drawn out of the induction heating unit toward a side on which the fixing roller or the heating roller is not disposed.
For example, FIG. 5 of JP-2003-338365-A illustrates a configuration in which a conductive wire is wired in a portion above an excitation coil 220, between straight parts on both sides of the excitation coil 220.
However, as illustrated in FIG. 2 of JP-2003-338365-A, the portion above the excitation coil 220 in which the conductive wire is disposed is a space between the excitation coil 220 and a unit cover, and more specifically, between arch cores 260 and a housing 270. Cooling air flows or passes through the space to cool down the excitation coil 51 in use of a cooling fan. If conductive wires of a coil thermostat and/or a temperature sensor are disposed in the space through which the cooling air passes, the conductive wires disrupt a current of the cooling air to reduce cooling efficiency.